Push button key block or keyboard assemblies are widely used to enter information in electrical and electronic systems. Telephone push button dials provide one usage of such devices to enter call control information into the telephone system. For computers and calculators, such devices act to enter data for manipulation within the calculator or computer.
The earlier key blocks in the telephone art used the principle of U.S. Pat. No. 3,109,071 issued to C. E. Mitchell et al. on Oct. 29, 1963. With electronic tone generators replacing the inductive-capacitive generators used with Mitchell key block, push button assemblies similar to those used in the computer arts become practical. For example, U.S. Pat. No. 4,029,916 issued to Chu on June 14, 1977 shows one form of pivoted individual button type usable for a telephone push button dial. A number of other patents issued covering computer key block assemblies applicable to telephone dials. The more relevant of these are U.S. Pat. Nos. 4,032,729 to Koistenen (June 28, 1977); 4,160,886 to Wright (July 10, 1979) and 4,096,364 (June 20, 1978).
In these patents are shown an array of push buttons individually hinged or resting in an enclosure. A push button when depressed acts against the effect of a spring to complete a contact path through a pair of stationary contacts, normally spaced apart, as for example, on a printed circuit board. The contact is a momentary one continuing for the period during which the button remains depressed. When the depressing force on the button is released, the spring restores the button to its normal condition and the electrical contacts are returned to an open circuit condition.